Self-aligned collar and strap formation for semiconductor devices
A method for fabricating a buried strap forms a dielectric collar along sidewalls of a trench. The trench is formed in a substrate. The trench is filled with a conductive material and the conductive material is recessed in the trench to expose a portion of the collar. A masking layer is deposited in the trench over the exposed portion of the collar. A portion of the masking layer is removed over one side of the collar and a portion of the collar is etched on the one side. A buried strap is formed on the conductive material, which connects to the substrate on the one side.
Latest Infineon Technologies AG Patents:
- SCR structure for ESD protection in SOI technologies
- Packaged semiconductor device and method for fabricating a packaged semiconductor device
- System and method for radar
- Sensor assembly for determining rotation about an axis and linear movement parallel to the axis
- Front bias magnetic speed sensor with true-power-on capability
1. Technical Field
This disclosure relates to semiconductor fabrication, and more particularly, to methods for forming a single sided buried strap on one side of the trench while protecting a collar dielectric on the other side of the trench.
2. Description of the Related Art
To reduce memory cell size and increase the density of devices formed on a semiconductor chip, vertical transistors have been developed. Memory devices, such as dynamic random access memories (DRAM) may include vertical transistors. Vertical transistors are formed by providing a trench in a substrate and forming a dielectric collar on sidewalls of the trench. A storage node is formed in the trench and recessed to provide access to substrate walls. A buried strap is formed in the recess by depositing a highly doped material in the trench. For vertical transistors, a single side buried strap may be employed. This single-sided strap is formed by methods, which may cause damage to the collar on the opposite side of the trench. In these cases, the collar would not provide adequate protection from the adjacent device.
Therefore, a need exists for a fabrication method which removes a portion of a dielectric collar to form a single-sided buried strap without damage to portions of the collar, which are to remain in the trench.
SUMMARY OF THE INVENTIONA method for fabricating a buried strap forms a dielectric collar along sidewalls of a trench. The trench is formed in a substrate. The trench is filled with a conductive material and the conductive material is recessed in the trench to expose a portion of the collar. A masking layer is deposited in the trench over the exposed portion of the collar. A portion of the masking layer is removed over one side of the collar and a portion of the collar is etched on the one side. A buried strap is formed on the conductive material, which connects to the substrate on the one side.
In other methods, the masking layer preferably includes nitride. The step of removing a portion of the masking layer may include patterning a cut mask for etching the masking layer. The step of removing a portion of the masking layer may include the steps of forming a polysilicon layer over the trench, doping and oxidizing the polysilicon layer in predetermined areas, removing the polysilicon layer in other than the predetermined areas and etching the masking layer the in accordance with the predetermined areas. The may further includes the step of forming isolation trenches in communication with the trench. The method may include the steps of oxidizing surfaces within the isolation trenches, lining the isolation trenches with a nitride layer, filling the isolation trenches with a dielectric material. The method may further include the steps of protecting portions of the nitride layer in communication with the trench during the step of removing a portion of the masking layer by employing surfaces oxidized in the step of oxidizing surfaces. The step of oxidizing surfaces may include forming an oxide between about 70 angstroms to about 90 angstroms in thickness. The step of forming a buried strap may include the steps of depositing a buried strap conductor in the trench and etching back the buried strap conductor.
A method for fabricating a one-sided buried strap, includes the steps of forming a dielectric collar along sidewalls of a trench, the trench formed in a substrate, filling the trench with a conductive material, etching isolation trenches in communication with the trench, oxidizing surfaces within the isolation trenches, lining the isolation trenches with a nitride layer, filling the isolation trenches with a dielectric material, recessing the conductive material in the trench to expose a portion of the collar, depositing a masking layer in the trench over the exposed portion of the collar, removing a portion of the masking layer over one side of the collar, etching a portion of the collar on the one side and forming a buried strap on the one side.
In alternate embodiments, the masking layer may include nitride. The step of removing a portion of the masking layer may include patterning a cut mask for etching the masking layer. The step of removing a portion of the masking layer may include the steps of forming a polysilicon layer over the trench, doping and oxidizing the polysilicon layer in predetermined areas, removing the polysilicon layer in other than the predetermined areas and etching the masking layer the in accordance with the predetermined areas. The method may include the steps of protecting portions of the nitride layer in communication with the trench during the step of removing a portion of the masking layer by employing surfaces oxidized in the step of oxidizing surfaces. The step of oxidizing surfaces may include forming an oxide between about 70 angstroms to about 90 angstroms in thickness. The step of forming a buried strap may include the steps of depositing a buried strap conductor in the trench and etching back the buried strap conductor.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.
This disclosure will present in detail the following description of preferred embodiments with reference to the following figures wherein:
The present invention provides methods for fabricating memory cells with vertical transistors. The present invention relates, in particular to the removal of a portion of a dielectric collar without damaging other portions of the dielectric collar in a deep trench structure. The methods of the present invention provide at least the following features: protects the collar while forming a buried strap, ensures that the collar width is equal to an active area width, reduces/eliminates dependence of isolation regions on active area-to-deep trench overlay, eliminates the need for an additional active area pad nitride layer for patterning the active area and reduces process complexity.
The present invention confines the buried strap in a lateral dimension by a self-aligned strap formation process. In devices which need a strap on one side of the trench, the present invention permits for the formation of the buried strap on the one side while protecting a collar formed in the trench on the other side. These features will become apparent by the following description of the present invention. The structures and materials employed herein are for purposes of illustratively describing the present invention. These illustrative examples, may be modified or changed within the scope of the present invention.
Referring now in specific detail to the drawings in which like reference numerals identify similar or identical elements throughout the several views, and initially to
A dielectric collar 18 is formed in trench 14. Collar 18 preferably includes a silicon oxide formed by, for example, a TEOS deposition or a LOCOS process, and node formation prior to or after the collar, as is known in the art. Trench 16 is filled with a conductive material 20, such as, doped polysilicon, to form a storage node 22. Material 20 is removed from a top surface of pad dielectric layer 14 by a planarization process (e.g., chemical-mechanical polishing (CMP).
An isolation trench hardmask 24 is deposited and lithographically patterned to provide an etch mask for the formation of isolation trenches. As shown in
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
Another embodiment of the present invention will now be described. This embodiment preferably includes dopant implantation and oxidation instead of a cut mask. Referring to
Referring to
Referring to
Referring to
Referring to
In a non-self-aligned scheme, the width of the collar must exceed a width dimension of an active area region to ensure lateral isolation. In other words, a sufficient amount of collar insulation must be present to ensure the sides of the trench are isolated from the regions outside the trench. The width of the collar in the non-self-aligned case must be large enough to account for misalignment tolerances between the active area (AA) region and the trench. Advantageously, in the self-aligned methods of the present invention, the collar width may be made exactly equal to the AA width and still provide good isolation. Since self-alignment is provided, the size of the collar and trench do not need to include larger dimensions to account for misalignment tolerances between the active area (AA) region and the trench.
Taking advantage of the alignment between active areas and deep trenches, permits additional advantages for the embodiments described above and for other memory cell designs. Referring to
Having described preferred embodiments for self-aligned collar and strap formation for semiconductor devices (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.
Claims
1. A method for fabricating a buried strap, comprising the steps of:
- forming a dielectric collar along sidewalls of a trench, the trench formed in a substrate;
- filling the trench with a conductive material;
- recessing the conductive material in the trench to expose a portion of the collar;
- depositing a masking layer in the trench over the exposed portion of the collar;
- removing a portion of the masking layer over one side of the collar;
- etching a portion of the collar on the one side; and
- forming a buried strap on the conductive material, which connects to the substrate on the one side.
2. The method as recited in claim 1, wherein the masking layer includes nitride.
3. The method as recited in claim 1, wherein the step of removing a portion of the masking layer includes patterning a cut mask for etching the masking layer.
4. The method as recited in claim 1, wherein the step of removing a portion of the masking layer includes the steps of:
- forming a polysilicon layer over the trench;
- doping and oxidizing the polysilicon layer in areas;
- removing the polysilicon layer in other than the areas; and
- etching the masking layer in accordance with the areas.
5. The method as recited in claim 1, further comprising the step of forming isolation trenches in communication with the trench.
6. The method as recited in claim 5, further comprising the steps of:
- oxidizing surfaces within the isolation trenches;
- lining the isolation trenches with a nitride layer;
- filling the isolation trenches with a dielectric material.
7. The method as recited in claim 6, further comprising the steps of:
- protecting portions of the nitride layer in communication with the trench during the step of removing a portion of the masking layer by employing surfaces oxidized in the step of oxidizing surfaces.
8. The method as recited in claim 6, wherein the step of oxidizing surfaces includes forming an oxide between about 70 angstroms to about 90 angstroms in thickness.
9. The method as recited in claim 1, wherein the step of forming a buried strap includes the steps of:
- depositing a buried strap conductor in the trench; and
- etching back the buried strap conductor.
10. A method for fabricating a one-sided buried strap, comprising the steps of:
- forming a dielectric collar along sidewalls of a trench, the trench formed in a substrate;
- filling the trench with a conductive material;
- etching isolation trenches in communication with the trench;
- oxidizing surfaces within the isolation trenches;
- lining the isolation trenches with a nitride layer;
- filling the isolation trenches with a dielectric material;
- recessing the conductive material in the trench to expose a portion of the collar;
- depositing a masking layer in the trench over the exposed portion of the collar;
- removing a portion of the masking layer over one side of the collar;
- etching a portion of the collar on the one side; and
- forming a buried strap on the one side.
11. The method as recited in claim 10, wherein the masking layer includes nitride.
12. The method as recited in claim 10, wherein the step of removing a portion of the masking layer includes patterning a cut mask for etching the masking layer.
13. The method as recited in claim 10, wherein the step of removing a portion of the masking layer includes the steps of:
- forming a polysilicon layer over the trench;
- doping and oxidizing the polysilicon layer in areas;
- removing the polysilicon layer in other than the areas; and
- etching the masking layer in accordance with the areas.
14. The method as recited in claim 10, further comprising the steps of:
- protecting portions of the nitride layer in communication with the trench during the step of removing a portion of the masking layer by employing surfaces oxidized in the step of oxidizing surfaces.
15. The method as recited in claim 10, wherein the step of oxidizing surfaces includes forming an oxide between about 70 angstroms to about 90 angstroms in thickness.
16. The method as recited in claim 10, wherein the step of forming a buried strap includes the steps of:
- depositing a buried strap conductor in the trench; and
- etching back the buried strap conductor.
Type: Grant
Filed: Jan 8, 2001
Date of Patent: Mar 21, 2006
Patent Publication Number: 20020090824
Assignee: Infineon Technologies AG (Munich)
Inventors: Venkatachalam C. Jaiprakash (Beacon, NY), Norbert Arnold (Chestnut Ridge, NY)
Primary Examiner: Benjamin L. Utech
Assistant Examiner: Kin-Chan Chen
Attorney: Slater & Matsil, L.L.P.
Application Number: 09/756,415
International Classification: H01L 21/311 (20060101);